South Africa has the largest number of people living with HIV/AIDS in the world and a rapidly aging population. In recent years, with expanded availability of ART, many adults are aging with HIV, and further, increasing numbers are acquiring HIV at older ages. Despite these population concerns, research on the impact of the HIV epidemic on older South Africans is scarce. The overall goal of HIV after 40 (HIV40) is to examine life course and contextual variation in HIV risk and protective behaviors in a rural sub-Saharan African population among a largely neglected demographic in HIV/AIDS research: adults aged 40-80. We seek funding to analyze data from the longitudinal Agincourt Health and Socio-Demographic Surveillance System (AHDSS) in rural South Africa and quantitative and qualitative data on HIV and sexual behavior among middle-aged and older adults nested within the AHDSS and collected by our research team. Our innovative and novel integrated multi-method dataset draws on five data sources including: (1) AHDSS data collecting annual censuses of 90,000 people in 27 villages followed from 1992-2014; (2) nested cross- sectional survey data of 5080 individuals (of whom 2080 are aged 40+) on sexual behavior with HIV and chronic disease biomarkers (2010-2011); (3) 60 nested life history interviews with HIV positive and negative adults aged 40-80 (2013); (4) community focus group data from 77 respondents (2013); and (5) key informant interview data from health workers in 3 local health clinics (2013). Guided by an innovative life course approach, we use these data to examine HIV risk and protective behavior in the transition from middle to older ages and the role of social context in shaping individual behavior. HIV40 is significant in its focus on life course variation and contex in HIV risk and protection in the transition to older ages. It offers cutting edge scientific advancement in the HIV and gerontology literature that will inform approaches to HIV prevention for older adults. It is also innovative in its use of a unique multi-method longitudinal and cross-sectional nested dataset. Our research will be conducted by a strong team of investigators with complementary strengths and collaborative experience working on the substantive areas and methods proposed here. Finally, we expect our work to contribute to and directly impact HIV prevention programming in rural South Africa by leveraging over twenty years of community relationships in Agincourt.